The contact lens art has long known the advantages of silicone polymers for use in contact lenses. Silicone polymers are transparent and highly permeable to oxygen, although use of these polymers in contact lenses sometimes causes difficulty in fabrication of lenses and often result in lenses with hydrophobic surfaces. It is known that the use of a methacrylate monomer containing a silicone moiety can be copolymerized with standard monomer utilized in conventional hard contact lenses, i.e., methyl methacrylate, to obtain a copolymer of varying hardness values depending upon the ratio of hard and soft monomers employed. Thus some attempts have been made in the art to produce hard oxygen permeable contact lenses. For example, U.S. Pat. No. 3,808,178 describes hard oxygen permeable contact lenses.
The silicone-containing polymers are normally soft materials with poor tear and rupture strength. Their use often causes machining problems in lenses since they impart low modulus to copolymers and cause other problems in that they are highly hydrophobic. Hydrophobic lenses are not wettable by tears and often result in vision and discomfort problems.
The oxygen permeability is directly related to the silicone content in contact lenses. It has been difficult to obtain high oxygen permeability while still maintaining other properties of a contact lens material at desired values when oxygen permeability is derived from the silicone content.